Color projection displays have become an essential element in today's imaging applications. Steady evolutionary advances in miniature high resolution display technology have not only made color projection pervasive, but have permitted the migration of color projection into working and leisure environments. These trends place increasingly stringent demands on existing projection technologies, which are either emissive devices, such as cathode-ray tubes (CRTs), or contain a high-resolution spatial light modulator (SLM) and an internal illumination source, such as Digital Micromirror Displays (DMDs) and liquid crystal displays (LCDs).
While conventional, self-luminous CRT projection systems are capable devices, they suffer from a number of shortcomings that may limit their future utility in projection imaging applications. For example, the broad spectral linewidth of phosphors results in poor color performance, while brightness is limited by a number of effects. Similarly, conventional LCD projection systems are limited in intensity because of the optical damage threshold of the SLM, the highly absorptive polarizers required, and the inefficient use of the internal illumination source. Additionally, DMDs are mechanically complex and must operate at high switching speeds in order to create grey scale via time sequential algorithms.
As a result of these and other shortcomings, the projected large-scale images produced by these conventional systems can appear dim and blurred. The dimness and blurring can be eliminated by providing more optical power and spectral purity. Both of these requirements can be fulfilled by, for example, laser sources.
Laser-based projection displays systems, however, can be cost prohibitive for leisure environments, and in particular for home use. Laser-based projection displays often illuminate areas in the 10.times.15 foot range, and are typically utilized in convention centers and other large forums. These laser-based systems produce large, bright, sharp images by incorporating several large lasers. These large laser sources can consume a significant amount of electrical power and space. The image production methods utilized by these laser-based projection systems often employ scanning techniques, for example a front or a back scanned illumination system, that requires additional subsystems. The additional subsystems can result in higher initial costs as well as other long-term costs due to maintenance associated with the subsystems.
It can therefore be appreciated that it would be desirable to develop a projection imaging system capable of home use that employs the advantages of the laser-based systems. The desirable projection imaging system should provide: 1) an efficient delivery of a bright image; 2) a high color purity; and 3) a minimal chromatic aberration.